Re: Returning range of inout objects from inout method

[Steven Schveighoffer via Digitalmars-d-learn]

On 7/25/20 8:26 AM, FreeSlave wrote:
I want to be able to return a range of const objects from the const 
object and a range mutable objects from the mutable object.

inout comes to mind, but not applicable in this case, because inout must 
be applied to the return type as whole, which does not make much sense 
for the range. Defining range of inout objects does not work too. See 
the example.

import std.range;
class A
{
     string name;
}

class B
{
     A[] _actions;
     ForwardRange!(inout(A)) byAction() inout { // can't instance this type
         import std.algorithm : filter;
         return inputRangeObject(_actions.filter!(a => a !is null && 
a.name.length));
     }
}

So how can I achieve the intended effect without code duplication? (like 
making separate mutable and const versions of the method).

You can't exactly. The limitation that inout cannot be applied to a 
struct member is a crappy limitation, one which I wish I never advocated 
for.

The only way to do this without code duplication (but with generated 
code duplication) is to template the byAction function on the type of 
`this`:

auto byAction(this This)() { /* same implementation */ }

Note that this ONLY works if your base range type is an array. If you 
have a custom range type, you need to parameterize that based on the 
constness of `This`.

-Steve